1. Field of the Invention
The present invention relates to an image processing apparatus in which image signals compressed in a horizontal direction by different compression ratios are subjected to aperture correction in which frequency characteristics are determined by the compression ratio.
2. Description of the Related Art
Conventionally, aperture correction is conducted on a currently available (NTSC) television signal having an aspect ratio of 3:4 to enhance the attenuated high-frequency components of the television signal which represent the contour thereof and thereby to improve the image quality.
FIG. 1 illustrates how the frequency characteristics of the television signal are improved by the above-described aperture correction operation. As shown in FIG. 1, the high-frequency component of a television signal, indicated by the solid line, is enhanced in the manner indicated by the broken line to improve the sharpness of an image obtained on the basis of that television signal.
However, when the aperture correction process conducted on the currently available television signals having an aspect ratio of 3:4 is applied to image signals which have been compressed in a horizontal direction by means of an anamorphic lens (a lens with cylindrical elements giving different magnifications in horizontal and vertical directions. In this embodiment, an image from an object is converted into an image which is expanded in the vertical direction by optically compressing the light from the object in the horizontal direction by means of the anamorphic lens), since the image signals have different energy distributions determined by the compression ratio, the process of expanding such compressed signals changes the frequency characteristics provided by the aperture correction process.
Practically, when a compressed image signal is received by a currently available television receiver having an aspect ratio of 3:4, the image quality of the expanded signal deteriorates due to the compression ratio of the received image signal.
FIG. 2 schematically shows a camera system which employs an anamorphic lens 31, a zoom lens 32, an imaging device 33 having an aspect ratio of 3:4, and a known signal processing signal 34 for processing the image signal output from the imaging device 33 in the known manner. FIG. 3 is a graph showing the relation between the compression ratio and the energy distribution of the compressed signal. FIG. 4 shows how the expansion process changes the energy distributions of the image signals on which the same aperture correction is conducted. As is apparent from FIG. 4, as the compression ratio increases, the energy level of the high-frequency components decreases. Thus, when image signals having various compression ratios are expanded, image quality deteriorates.